autotest: clear context before looking for GPS type

Will clarify the output as currently we look through the text messages for all of the previous gps types when trying to find the detection message for the current GPS

Tools/autotest/common.py

@@ -12187,13 +12187,14 @@ switch value'''
             (8, "NOVA", 15, "NOVA"),  # no attempt to auto-detect this in AP_GPS
             # (9, "FILE"),
         ]
+        self.context_collect("STATUSTEXT")
         for (sim_gps_type, name, gps_type, detect_name) in sim_gps:
             self.start_subtest("Checking GPS type %s" % name)
             self.set_parameter("SIM_GPS_TYPE", sim_gps_type)
             if gps_type is None:
                 gps_type = 1  # auto-detect
             self.set_parameter("GPS_TYPE", gps_type)
-            self.context_collect("STATUSTEXT")
+            self.context_clear_collection('STATUSTEXT')
             self.reboot_sitl()
             self.wait_statustext("detected as %s" % detect_name, check_context=True)
             n = self.poll_home_position(timeout=120)